Automated Optical Measurement System To Determine Semiconductor Properties

ABSTRACT

Described are devices and methods for measuring semiconductor materials, devices, circuits, and systems. The device includes a probe head that accepts multiple optical assemblies. At least one optical assembly provides a light source, and at least one optical assembly provides a detector. Both are coupled to the probe head. The optical assemblies may be manually or automatically adjustable using kinematic mounts, and may include optical fibers for conveying light to and from a sample. Each optical assembly may include a lens stack or an objective. Illumination and collection assemblies may share a common focal point, and different subsets of assemblies may share different focal points. The device may include a sample bed for imaging multiple samples at once, and may be coupled to a control system for automatically positioning the samples and/or the optical assemblies.

BACKGROUND

Traditionally, semiconductors used for electronic and optoelectronicapplications are optimized using a top-down engineering approach,wherein a single device is built, tested, and afterwards studied todetermine where improvements in performance can be made. Oftentimes,more than one device is fabricated in order to obtain statistics or tocompare different processing conditions. This common practice istime-intensive, inefficient, and expensive.

SUMMARY

Described herein is an automated, optical measurement system (or “tool”)for determining various properties of semiconductor samples. The tool iscapable of handling multiple samples and concurrently or simultaneouslymeasuring a broadband optical response of a photoactive layer, such asphotoexcited carrier recombination rates and diffusion length. Unlikethe known prior art, the tool described herein is a single instrumentthat allows a user to “plug and play” (i.e. freely substitute) their ownlight source (e.g. a laser) and detection systems (e.g. imagingsensors). The tool is capable of accurately predicting deviceperformance by analyzing only half of the total layers in the completeddevice.

Also, this tool allows the user to evaluate materials to a performancelimit (e.g. a maximum theoretical performance limit). Traditionally,materials are compared to reference or calibration devices, which cantake a long time to fabricate. Theoretical limits, on the other hand,can provide users (e.g. researchers) an advantage in the materials anddevice optimization processes. It is noted that additional userexperience in fabricating high-quality devices can provide helpfulinformation and processing constraints that could facilitate even moreefficient workflow.

Thus, one embodiment of the concepts, techniques, and systems describedherein is a device for optically measuring properties of a semiconductorsample, the device comprising a probe head configured to accept aplurality of optical assemblies; one or more optical assemblies, eachcomprising a light source, coupled to the probe head and configured todirect light toward the sample; and one or more optical assemblies, eachcomprising a detector, coupled to the probe head and configured todetect light from the one or more light sources.

Some embodiments further include a sample bed for concurrently acceptingmultiple samples.

In some embodiments, the optical assemblies comprise a broadband opticallight source and optics for detecting a response of a semiconductor.

In some embodiments, the optics for detecting a response of asemiconductor comprises optics for detecting a response of asemiconductor having a photoactive layer.

In some embodiments, the optical assemblies comprise a broadband lightsource and a detector configured to detect signals from the broadbandlight source.

In some embodiments, the optical assemblies comprise a monochromaticlight source and a detector configured to detect signals from themonochromatic light source.

In some embodiments, the optical assemblies comprise a plurality oflight sources and a detector that is configured to detect signals frommultiple ones of the plurality of light sources.

In some embodiments, a number of light sources coupled to the probe headequals a number of detectors coupled to the probe head.

In some embodiments, each detector is configured to detect light from acorresponding one of the light sources.

Another embodiment is a probe head comprising means for concurrentlymaking measurements of a semiconductor using one or more broadband lightsources and one or more monochromatic light sources.

In some embodiments, at least one of the one or more monochromatic lightsources is a laser light source.

Another embodiment is a measurement system comprising an interchangeableoptical probe head configured to accept multiple sources and multipledetectors thereby allowing for concurrent measurements and imaging onmultiple samples.

Some embodiments further include a processor configured to perform datamanagement and/or a data analysis methodology applicable to anyoptically active material.

Another embodiment is a method of determining physical parameters of asemiconductor sample, the method comprising: accepting the semiconductorsample; concurrently exposing the semiconductor sample to a plurality oflight sources; concurrently detecting light from the plurality of lightsources; and determining a range of physical parameters of thesemiconductor sample.

In some embodiments, accepting the semiconductor sample comprisesaccepting a plurality of partially completed semiconductors; anddetermining the range of physical parameters of the semiconductor samplecomprises determining a range of physical parameters of the plurality ofpartially completed semiconductors.

The concepts, systems, devices and techniques described herein findutility in a variety of areas including, but not limited to:semiconducting materials used for solar cells, light-emitting diodes,integrated circuits, photodetectors, lasers, etc. It had been recognizedthat such semiconducting materials are traditionally difficult tooptimize because performance losses depend on several factors.Pinpointing these factors typically requires multiple measurements overseparate instruments, making the process time-intensive. The concepts,systems, devices and techniques are directed towards a large-area,automated characterization system (also sometimes referred to herein asan “automated tool” or more simply a “tool”) capable of performingseveral distinct measurements with the same mechanical configuration(i.e. the same setup) and extracting a range of physical parameters. Inembodiments, such parameters may be provided as inputs to a system thatpredicts performance before completing the device. Overall, theconcepts, systems, devices and techniques described herein save bothtime and cost and provides new physical insights that guide rationaldevice optimization.

Accordingly, the system described herein, is a system capable ofhandling/measuring/analyzing one or more samples with less (and ideallyminimal) human interaction compared with prior art systems. Inembodiments, the tool is capable of concurrentlyhandling/measuring/analyzing properties of multiple, different samples.

In embodiments, the samples may be semiconductor materials or devices(collectively referred to herein as a “semiconductors”). In embodiments,the tool may measure a series of specific properties (characteristics)of one or more semiconductors. The tool allows the measurements to bedone concurrently on one or more semiconductor materials or devices. Inembodiments, the measured properties of the one or more semiconductormaterials or devices may be used as inputs into models used to estimateor predict performance limits (e.g. theoretical performance limits) ofthe one or more semiconductor materials or devices. In embodiments, theone or more semiconductor materials or devices may include, but are notlimited to, solar cells, light-emitting diodes, integrated circuits,photodetectors, lasers, to name but a few examples.

In embodiments, the tool allows the measurements to be done concurrentlyon one or more partially completed semiconductor materials or devices.In embodiments, the measured properties of the partially completedsemiconductor materials or devices may be used as inputs into devicemodels(e.g. detailed-balance device models) which may estimate orpredict performance limits (e.g. theoretical performance limits) of acompleted semiconductor material or device. In embodiments, thecompleted one or more semiconductor materials or devices may be include,but are not limited to: solar cells, light-emitting diodes, integratedcircuits, photodetectors, lasers, to name but a few examples.

In embodiments, the tool is capable of making multiple measurements atdifferent points in time (or at different portions of one or morefabrication steps) throughout a device fabrication process.

In embodiments, the tool comprises a multimodal probe head design whichallows the tool to concurrently (or in some cases simultaneously)measure with both broadband as well as monochromatic (i.e. laser)sources with. Concurrent and/or simultaneous measurement allows forrapid acquisition of data sets (which may be relatively large) used toidentify performance-limiting regions. In embodiments, the multimodalprobe head may be guided by machine vision. A controller coupled to themultimodal probe head coupled with machine vision allows the tool to beautomated. The tool may thus result in a significant reduction in theuser time incurred for traditional measurements. The tool has a modulardesign where external light-sources or detection systems available to auser can be easily integrated with the tool, providing both versatilityand cost-savings. Light sources, detectors, and timing electronics cancomprise >90% of the total instrument cost. The system described hereinallows the user to “plug-and-play” with light sources and/or detectorsincluding existing commercially available light sources and/or detectors

Embodiments of the tool may be used at least for the following,illustrative purposes: (A) Bulk Performance Measurements; (B) BulkStability Measurements; and (C) Imaging Measurements.

Bulk Performance Measurements may include: (A1) automated acquisition ofsingle measurements including transmittance, reflectance, steady-statephotoluminescence, and time-resolved photoluminescence on a single ormultiple samples; and (A2) automated acquisition of simultaneous andsequential measurements of transmittance, reflectance, steady-statephotoluminescence, and time-resolved photoluminescence paired with dataanalysis to extract material recombination rate constants, interfacialrecombination rates, surface recombination velocities, diffusionlengths, quantities related to the dielectric function (i.e. absorptioncoefficient), and sample thickness; which are then used as inputs intotheoretical device models for a single or multiple samples.

Bulk Stability Measurements may include: (B1) in-situ monitoring oflight or thermal induced degradation; (B2) monitoring of chemical andstructural changes with optical probes over extended periods of time(i.e. months).

Imaging Measurements may include: (C1) the probe head (described infurther detail hereinbelow) can be equipped with imaging optics (i.e. anobjective) to perform both macro and microscopic measurements includingphotoluminescence, electroluminescence, and light-beam induced current(LBIC) imaging. Defects from processing and poor interlayer contacts canbe quickly identified, isolated, and optimized.

The tool described herein may have an interchangeable optical probe headallowing for simultaneous measurements and imaging on multiple samples.The tool's design is modular allowing users to integrate their own lightsources and detectors into the setup which, in some cases, can reduce(and in some cases significantly reduce) the total system cost. Bycontrast, known commercial instruments for performing common physicalmeasurements can only measure one sample at a time.

In embodiments, the tool comprises a processor configured to performdata management and/or a data analysis methodology that is broadlyapplicable to any optically active material.

The first demonstrations of this tool have revealed several unexpectedresults. For example, in embodiments, a solar cell's performance can bepredicted by depositing and measuring only 3 of 6 total layers,saving >60% of the typical time to complete a full device. Inembodiments, using the automated tool described herein, it is found thata user may, on average, save 8 minutes of instrument interaction timeper sample. For a common solar cell device batch of 16 samples, thisequates to approximately 2 hours of time savings for the user.

This Summary is provided to introduce a selection of concepts insimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key or essentialfeatures or combinations of the claimed subject matter, nor is itintended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages will beapparent from the following more particular description of theembodiments, as illustrated in the accompanying drawings in which likereference characters refer to the same parts throughout the differentviews. The drawings are not necessarily to scale, emphasis instead beingplaced upon illustrating the principles of the embodiments.

FIG. 1 is a block diagram of a system for characterizing a semiconductorand capable of measuring multiple semiconductor parameters(simultaneously if necessary) with different light sources anddetectors;

FIG. 2A is a front isometric view of a system for characterizing asemiconductor and capable of simultaneously measuring multiplesemiconductor parameters;

FIG. 2B is a rear isometric view of a system for characterizing asemiconductor and capable of simultaneously measuring multiplesemiconductor parameters;

FIG. 3A is a rear isometric view of a system for characterizing asemiconductor and capable of simultaneously measuring multiplesemiconductor parameters illustrating a probe head and optic assemblylocations;

FIG. 3B is an enlarged view of the probe head and optic assemblies ofFIG. 3A with an example of a signal collection geometry with one lightsource and two detecting systems;

FIG. 4 is a partially exploded view of a pair of optical assembliesdisposed over a probe head;

FIG. 5 is an isometric view of a probe head;

FIG. 6 is an isometric view of three optical assemblies disposed over aprobe head;

FIG. 7A is an enlarged view of an optical assembly;

FIG. 7B is an isometric view of the optical assembly of FIG. 7A having alight shield thereof removed to reveal a kinematic coupling;

FIG. 8 is an isometric view illustrating an alternate embodiment of aprobe head design;

FIG. 9 is a top view of four optical assemblies disposed over a probehead;

FIG. 10A is a top view of a probe head embodiment configured to holdthree optical assemblies;

FIG. 10B is a top view of a probe head embodiment configured to holdeight optical assemblies;

FIG. 11A is an isometric view illustrating an alternate embodiment of aprobe head and optical assembly design with the optical assembly havinga different mounting scheme for the kinematic mount and an objectiveassembly having a lens stack (e.g. as illustrated in FIG. 4 ) replacedwith an objective;

FIG. 11B is an isometric view illustrating that an objective can be usedto direct light to and from the sample in replacement of the lens stack;

FIG. 12A is an isometric view of a system having a probe head with anadjustable portion configured to accept a lens stack or an objective ofan optical assembly;

FIG. 12B is a cartoon side view of FIG. 12A illustrating an effect ofadjusting the optical assembly;

FIG. 13A is an isometric view of a system in which focal points of thesource and collection optics are aligned (i.e. directed toward a singlefocal point);

FIG. 13B is an isometric view of a system in which focal points of thesource and collection optics are purposely displaced (i.e. the systemhas multiple focal points);

FIG. 14 is a top view of an alternate embodiment of a probe head inwhich collection optics and illumination optics are oriented such thattheir positions on the probe head can be independently changed;

FIG. 15 is a side view of an alternate embodiment of a probe head inwhich at least portions of the optical assembly are perpendicular to thesample;

FIG. 16 is a side view of an alternate embodiment of a system in whichelectrical contacts are disposed on a probe head;

FIG. 17 illustrates solar cells in various stages of processing that canbe measured to probe their intrinsic, interfacial, and extrinsic factorsleading to energy loss in the device or which otherwise impact deviceperformance;

FIG. 18 is a plot of user instrument interaction time vs. number ofsamples for a typical collection of photoluminescence data from asemiconductor;

FIG. 19A is a plot of transmittance and reflectance vs. wavelength usedto calculate an absorptivity spectrum of a sample;

FIG. 19B is a plot of absorptivity vs. wavelength computed using thetransmittance and reflectance values in FIG. 19A;

FIG. 20A is a plot of steady state photoluminescence (PL) vs. wavelengthand b) time-resolved PL decay trace obtained by using differentconfigurations of an embodiment;

FIG. 20B is a plot of time-resolved photoluminescence (PL) vs. time;

FIG. 21A is a plot of photoluminescence (PL) intensity vs. time usingvarious configurations of an embodiment;

FIG. 21B is a reduced Chi-squared surface plot (i.e. error) with acircle marking a global minimum; and

FIG. 22 is a flowchart of a method of determining physical parameters ofa semiconductor sample according to an embodiment.

DETAILED DESCRIPTION

Referring now to FIG. 1 , a system for characterizing a sample (e.g.semiconductor) and capable of measuring multiple sample (e.g.semiconductor) parameters (simultaneously, if necessary) includes aprobe head configured to accept multiple different optical assemblies,each of which may include one or more light sources and one or moredetectors. Sources may include, but are not limited to, two or more of:photoluminescence (PL) sources, electroluminescence (EL) sources, laserbeam induced current (LBIC) sources and light emitting diode (LED)source. Other light sources may, of course, also be used. The particularcombination of light sources to use in any application depends upon avariety of factors including, but not limited to, the type of samplebeing measured.

One or more detectors, capable of detecting signals from the sources aredisposed to detect the signals. The detected signals (which may be rawdata or data processed by the detectors) are provided to a performancemetrics processor (not shown) which computes or otherwise determinesperformance metrics. A control system is coupled to the variouscomponents to coordinate operation of the various components. Inparticular, a motion controller controls motion of a platform on which asemiconductor under test may be disposed. The motion controller mayimplement motion logic via a processor that is the same or a differentprocessor as the performance metrics processor.

Referring now to FIGS. 2A and 2B, a system for characterizing asemiconductor includes a frame, a transport assembly, and a probe headcoupled to one or more optical assemblies. In embodiments, the probehead may be coupled to the frame and the one or more optical assembliesmay be coupled to the probe head (as shown in more detail in subsequentFigures). In embodiments, the one or more optical assemblies may becoupled to the frame and to the probe head. In embodiments, both the oneor more optical assemblies and the probe head may be coupled to theframe. The optical transport assembly comprises a platform configured toaccepts one or more samples (e.g. one or more semiconductors) and movethe one or more samples to a position at which the probe head/opticalassembly may measure the one or more samples. A motion controller (whichmay implement motion logic via a processor) controls motion of theplatform on which one or more samples under test may be disposed.

An advantage of the tool's design is its flexibility and the range ofequipment with which it can be paired. The three subcomponents of thetool—the light source, probe head, and detection equipment—are eachdesigned for modularity. Further explanation of the modularity of thesesystems and the process flow is described below, starting from the lightsource, to the optical fiber, to the probe head, to signal collectionthrough another optical fiber, and finally to the detection equipment.

The light source can vary depending on the tool's application andmultiple light sources can be used simultaneously. For example, amonochromatic light source, such as a laser, could be used alongside abroadband light source such as a xenon arc, tungsten, or metal halidelamp. Any of these light sources could also be used independently ifdesired. The flexibility in light source and detector selection iscoordinated with control software and accompanying microelectronics.Thus, the optical assemblies may comprise a plurality of light sourcesand a detector that is configured to detect signals from multiple onesof the plurality of light sources. Alternately, a number of lightsources coupled to the probe head may equal a number of detectorscoupled to the probe head, and each detector is configured to detectlight from a corresponding one of the light sources.

Referring now to FIGS. 3A and 3B, shown is an embodiment of the toolthat employs a single set of illumination optics and multiple collectionoptics. Threaded mounts are placed in axial symmetry along a focal planebelow the probe head center. As such, illumination and detection opticsare placed equidistantly at complementary angles so that each opticalconfiguration shares the same focal point (as also shown in FIG. 13A anddiscussed below). This focal point is just below the base of the probehead in order to avoid collision with the sample, while still shieldingexternal light that would impact the signal-to-noise ratio. Thisconfiguration allows for collection of reflected light as well asemission.

Other embodiments of this tool can collect sample signals at obliqueangles to quantify light directionality (as also shown in FIGS. 12A-12Band discussed below). These data can be filtered spatially or spectrallyto avoid signal cross-talk along different points of the optical train.The incorporation of multiple mounting points for illumination andcollection optics (as shown in FIG. 5 and discussed below) gives thetool the capability of collecting a combination of data simultaneously.This not only increases throughput, it also allows for the applicationof device models that can process multiple data types.

The probe head also interfaces with the motion systems of the tool. Theprobe head is capable of translation in all three Cartesian axes (i.e.x, y, and z). This motion may be guided by a control processor whichmay, for example, execute control software, which can detect samplelocations and direct the probe head to each sample autonomously, usingtechniques known in the art. This allows the tool to analyze multiplepoints on a single sample, or multiple samples, in a single run. As aresult, the tool may be used to reduce the user-time required comparedto traditional methods (as shown in FIG. 18 and discussed below).

Thus, in FIGS. 2A-3B is shown a device for optically measuringproperties of a semiconductor sample. The device includes a probe headconfigured to accept a plurality of optical assemblies. The device alsoincludes one or more optical assemblies, each comprising a light source,coupled to the probe head and configured to direct light toward thesemiconductor sample. And the device includes one or more opticalassemblies, each comprising a detector, coupled to the probe head andconfigured to detect light from the one or more light sources. Thedevice includes a sample bed for concurrently accepting multiplesamples.

As may be seen in FIG. 4 (and FIGS. 7A, 7B, 11A, 11B, and 12A discussedbelow), the light source may be coupled to the probe head via an opticalfiber such that light may be transmitted from the light source to theprobe head via the optical fiber. The optical fiber is selected based oncharacteristics such as appropriate signal attenuation, spectral window,and permitted optical modes depending on the measurement type. Thismodularity further contributes to the overall flexibility of the toolsince light sources and detection equipment can be freely substituted.As a result, these external components can remain a part of otheroptical systems and still be utilized for this tool when needed.

As the light source enters the probe head, it is adjusted and focused tomeet the needs of the application. The specificadjustment/focusing/tuning needs vary for each application based uponthe light source, sample, and characterization tests being performed.The probe head accounts for the range of tuning needs through theimplementation of a modular optics mounting strategy. In embodiments,the optics may utilize industry-standard threads for easyinterchangeability while remaining compatible with the threaded mountsplaced on the base of the probe head. This allows for a variety ofoptical components such as lenses, lens tubes, and light filters to beplaced between the input optical fiber and the sample. The modularity ofoptical components also applies to the collection optics which collectand filter the signal from the sample and relay it through an outputoptical fiber.

The output optical fiber can carry the signal to a variety of detectionsystems. These systems are necessary intermediaries that allow signalfrom the sample to be collected and transformed into meaningful data.The detection systems could include a single photon avalanche photodiode(SP-APD), a photo-multiplier tube (PMT), a charged coupled device (CCD),and/or an oscilloscope. Modular software design allows for code wrappersto be integrated into the tool's main software that are capable oftranslating and controlling detection equipment through their nativesoftware library. As a result, the characterization tool can be madecompatible with a wide range of detection equipment models andmanufacturers.

Referring now to FIG. 4 , a probe head has an illumination opticalassembly (or more simply “illumination optics”) and a collection opticalassembly (or more simply “collection optics”) coupled thereto. It isappreciated that the probe head shown in FIG. 4 may accept more thanjust these two assemblies, and that embodiments of the probe head may beconfigured to accept other numbers of assemblies (e.g. as shown in FIGS.9, 10A, and 10B described below). In the illustrative embodiment of FIG.4 , the probe head is provided having six (6) couplings, only three ofwhich are visible and only two of which are used.

The illumination optics comprise a kinematic mount coupled to akinematic mount coupling, and a lens stack coupled to the kinematicmount. The optical fiber (which is not properly considered a part of theillumination optics) has a first end configured to be coupled to a lightsource (not shown) and a second end configured to be coupled to thekinematic mount via a fiber adapter. In embodiments, the kinematic mountis coupled to the kinematic mount coupling and a first end of the lensstack is coupled to the kinematic mount and in optical communicationwith the optical fiber. A second end of the lens stack is coupled to theprobe head and disposed over an aperture provided in the probe head suchthat an optical signal path extends from the light source, through theaperture and optical fiber, to contact the sample (not shown).

It should be noted that all parts aside from the kinematic mountcoupling and probe head may be provided as off-the-shelf components.This facilitates interchangeability and use of optical components thatlaboratories and other entities are likely to already have on hand.

As will be described in further detail below in conjunction with FIGS.5-16 , the kinematic mount coupling and probe head are custom designedcomponents that are integral to the functionality of the system.

Referring to FIG. 5 , the multimodal probe head (sometimes referred toherein as an optical probe head) serves as a mobile and modular mountingpoint for optical components (e.g. the optical assembly) necessary toperform characterization tests. As noted above, optical fibers are usedto carry light signals both in and out of the probe head. This allowsfor a system in which the light source and detection equipment can beplaced outside of the tool-leaving them accessible and offeringmodularity.

In embodiments, the probe head may be directly connected to one or morelinear motion elements and can be positioned with respect to a samplefor testing. Various adaptations can be made to the probe head tointroduce further features and functionality. It is important to notethat, in embodiments, the probe head is designed and configured tofacilitate replacement (i.e. one probe head may be rapidly replaced byanother probe head). This allows users to reduce the amount of setuptime between various optical configurations by simply attaching apre-aligned probe head if desired. In this example embodiment, the probehead comprises a mounting structure configured to couple to railsprovided in a measurement system such as one of the systems describedabove in conjunction with FIGS. 1-3B.

Referring now to FIG. 6 , a probe assembly is comprised of a probe headand optics for both illumination and collection. The purpose of thisassembly is to position the optics relative to a sample while allowingfor localized optical tuning (via filters and lenses) and adjustment foroptical alignment at the desired focal point.

The illumination optics (also sometimes referred to as an “illuminationoptical assembly”) receives light from a light source via an opticalfiber and directs the light toward a sample and a pair of collectionoptical assemblies (also sometimes referred to as “detection opticalassemblies”) comprising collection optics disposed to collect lightreflected or otherwise re-directed from the sample. Thus, inembodiments, it is desirable that the focal point of the detectionoptics be at or near the focal point of the input optical assembly.

Referring now to FIGS. 7A and 7B, after input and output optical fibershave been attached to the probe head and optical assemblies, a varietyof off-the-shelf optical components can be used to customize the tuningand filtering of the light directed at a sample and the resultingsignal. In order to ensure alignment in and out of each optical fiber,the system includes a kinematic mount assembly (also sometimes referredto as a kinematic mount adapter) comprising a kinematic mount coupling.In ordinary operation, a light shield may be provided to excludeexternal light sources from the inner workings of the optical assembly.The light shield is shown in FIG. 7A, and removed in FIG. 7B to revealthe kinematic mount coupling

In embodiments, the kinematic mount adapter threads directly to theoptics configuration connected to the probe head. A kinematic mount inwhich the fiber port is attached is then fixed to the coupling withclearance for adjustment of the fiber. The kinematic mount is attachedin such a manner that the optical fiber can be adjusted for tip, tilt,pitch, yaw, and both x-and y-directions independently from the fixedoptical components that are attached directly to the probe head body.This may be important for calibrating optics and correcting formanufacturing inaccuracies.

Other embodiments of the tool include an electronically actuated fibermounting system that automatically adjusts the alignment in all sixdegrees of freedom. Optical fiber alignment thumbscrews can be actuatedwith positioning motors. This allows an autonomous calibration sequenceto get proper optical alignment, and testing in which the focal point ofthe source or collection optics is dynamically changed. This permitsanalyzing localized response of a sample as a function of distance fromthe source focal point. Multiple illumination and detection opticsconfigurations can also be used at once.

Referring now to FIG. 8 , shown is an isometric view illustrating analternate embodiment of a probe head design. In this embodiment, probehead positioning elements are decoupled from the probe head itselfthrough a “hanging” mounting fixture. Also, the probe head is free oflinear motion elements (no mounting features for guide rods orbearings). Aside from creating a more conducive volume for analternative embodiment, this probe head design also allows for probeheads to be “hot swapped”. The probe head is attached with a simplebolted connection that can be unscrewed so a different probe head can beput in place. This offers flexibility to integrate the other potentialembodiments shown in later Figures, and also allows users to havepre-configured probe heads (i.e. having different optical assemblies inuseful combinations) that can be swapped in if needed.

Thus, in FIG. 8 is shown a measurement system comprising aninterchangeable optical probe head configured to accept multiple sourcesand multiple detectors thereby allowing for concurrent measurements andimaging on multiple samples. The measurement system may be coupled to aprocessor configured to perform data management and/or a data analysismethodology applicable to any optically active material, as describedabove.

Referring now to FIG. 9 , shown is a top view of four optical assembliesdisposed over a probe head. FIG. 9 illustrates four (4) optics mountingpoints. As illustrated by FIGS. 10A, 10B below, the number of opticalassemblies which can be accepted by a probe head can increase ordecrease to accommodate the desired number of illumination andcollection optics needed for particular applications. The onlylimitation is physical (Le. available volume in which to mount thecomponents, and working distances required by the optics). It should ofcourse, be appreciated that not all mounting points need to be occupiedfor operation. Illustratively, FIG. 10A is a top view of a probe headembodiment configured to hold three optical assemblies and FIG. 10B is atop view of a probe head embodiment configured to hold eight opticalassemblies.

FIG. 11A is an isometric view illustrating an alternate embodiment of aprobe head and optical assembly design with the optical assembly havinga different mounting scheme for the kinematic mount, and an objectiveassembly having its lens stacks (e.g. as illustrated in FIG. 4 )replaced with individual objectives. This embodiment comprises spacerblocks which couple the kinematic mount to the probe head, of which onlyone is identified in FIG. 11A. Their geometry determines the distancefrom the objective to the sample. This component could be madeadjustable or motorized as shown in other embodiments that include thekinematic mount coupling. A kinematic mount may be the same as, orsimilar to, that described in conjunction with above embodiments, butnow serves as the sole mounting point for both the optical fiber andobjective. An objective may be used in place of the lens stack (asdescribed in some embodiments above). An objective could also be used inthe previous embodiments.

In this example embodiment, the probe head comprises a dome shape. Thisallows for a mounting scheme in which the kinematic mount serves as thesole mounting point for both the objective (or lens stack) and opticalfiber.

Thus, the embodiment of FIG. 11A illustrates a different mounting schemefor the kinematic mount. It also shows the lens stack replaced with anobjective. These changes allow the kinematic mount to be the onlyattachment point for both the objective and optical fiber. As a result,the optical fiber is in a fixed position relative to the objective andthe whole assembly is adjusted via the kinematic mount. It should alsobe noted the kinematic mount coupling is no longer needed in this designand has been replaced by the spacer blocks (green) which serve to setthe distance from the objective to the focal point on the sample towithin the working distance of the objective.

Referring now to FIG. 11B, as a follow up to FIG. 11A, an objective canbe used to direct light to and from the sample in replacement of thelens stack. The ability to use an objective will be important for givingthe characterization tool imaging capability. As such, objectives may beused quite frequently when the tool is deployed into research andindustry applications. Thus, an objective may be used in place of a lensstack and mounted directly onto the kinematic mount in the configurationshown.

Referring now to FIG. 12A, shown is a probe head having an adjustableportion configured to accept a lens stack or an objective of an opticalassembly. Adjustment allows the incident angle of the optics to bemodified to a user's needs. This embodiment illustrates the potentialfor angular adjustment of the optics at the probe head mounting point.The angle at which the lens stack mounts to the probe head can bevaried, and this angle may be configurable using built-in adjustmentfeatures on the probe head.

Referring now to FIG. 12B, shown is a cartoon side view of FIG. 12Aillustrating an effect of adjusting the optical assembly. As notedabove, adjustment would allow for incident angle of the optics to bedetermined by the user.

Referring now to FIG. 13A, shown is a system in which focal points ofthe source optics (left) and collection optics (top and right) arealigned, i.e. directed toward a single focal point. It should, ofcourse, be appreciated that focal points of the optics do notnecessarily need to be aligned. In alternate embodiments the focal pointof the source and collection optics could be purposely displaced tomeasure sample response as a function of distance from the source focalpoint.

Referring now to FIG. 13B, shown is a system in which focal points ofthe source and collection optics are purposely be displaced. Inembodiments, multiple focal points may be achieved by adjusting at thekinematic mount or at the lens stack mounting point on the probe head.It is noted that the modularity of the probe head design permits subsetsof illumination and collection optics mounted on a single probe head toshare the same focal point while other subsets share a different focalpoint. Thus, a probe head can accommodate multiple focal points sharedby different source and collection optics that are analyzedsimultaneously.

Referring now to FIG. 14 , shown is an embodiment of a probe head inwhich collection optics and illumination optics are oriented such thattheir position on the probe head can be changed. Multiple focal pointscould also be achieved with a probe head as shown in FIG. 14 . In thisinstance, the collection optics and illumination optics are orientedsuch that their position on the probe head can be changed. Thistranslation can be delivered either manually or autonomously viamotorized linear guides. The optics may have independent linear travelbuilt into the probe head.

Referring now to FIG. 15 , shown is an embodiment of a probe head inwhich at least portions of the optical assembly are perpendicular to thesample. In this embodiment, the illumination source and collected signalwould be carried through the same objective or lens stack. The collectedsignal would need to be optically filtered and potentially segregatedvia a beam splitter. This orientation would be particularly useful forimaging samples and could be used alongside other optics mounted to theprobe head such as those shown in angled orientations in previousFigures.

Referring now to FIG. 16 , shown is a side view of an alternateembodiment of a system in which electrical contacts are disposed on aprobe head. The integration of electrical contacts on the probe headallows for a current to be passed through a sample at specific points,thus for the analysis of a sample's electroluminescence, and could bepaired with embodiments from previous Figures to enableelectroluminescence imaging. A spring plunger mechanism (or othersimilar feature) ensures physical contact is made with the samplewithout damaging the electrical contacts or sample. Electrical contactsmay be mated to the surface of the sample, and a current applied. Theresulting light emitted by the sample can then be analyzed with thetypical optics shown in previous Figures.

Referring now to FIG. 17 , shown is an example of different stages inthe assembly process for a solar cell, which involves deposition of aphotoactive layer on top of an electronically insulating piece of glass,then subsequent deposition of an electron or hole (p-type) transportlayer (ETL and HTL, respectively), and finally the deposition of themetal contact to complete the device. Each stage of assembly may providea sample for separate evaluation by the tool to understand the bulkenergy losses within the semiconducting layer, at the charge transportlayer/photoactive layer interfaces, as well as through parasiticabsorption (due to poor reflectivity) at the back metal contact. It isappreciated that devices other than solar cells are constructedaccording to similar processes, and thus may be analyzed by the tool ateach stage in a similar manner.

In embodiments, the system may include software which may reduce theamount of human interaction typically required to perform a set ofmeasurements as well as reduce the tool's manufacturing cost. Usingmachine vision, the software may identify samples and suggest collectionpoints, which can be manually approved or automatically executed.

FIG. 18 is a plot of user instrument interaction time vs. number ofsamples that compares manual sampling and data collection known in theart to automated sampling and collection in accordance with anembodiment. Prior commercially available instruments are logisticallytime intensive and require loading and unloading multiple samples,setting data acquisition parameters, optical alignment, and additionalsoftware interaction. For example, based on a user survey in ourresearch lab, collecting time-resolved photoluminescence data for onesample typically takes about 8 minutes of user-instrument interfacingtime, which scales linearly with the number of samples as shown in FIG.18 . Thus, collecting data for 20 samples requires about 160 minutes. Bycontrast, the automated tool described herein only requires an upfrontinterface time of 4 minutes, and sampling may be completed within about1 minute. Paired with the tool, software thus reduces user interactiontime and simplifies the labor required to loading samples once, theninitiating data collection.

The modular design of embodiments allows for multiple light source anddetector configurations. For example, a broadband light source may beused to collect spectrally dependent information with regards to thephotoactive layers. Different embodiments involve the broadband lightsource passing through a spectral filter (i.e. diffraction grating)before or after interacting with the sample.

FIG. 19A shows example data sets of transmission and reflection spectra,collected with optical components of the tool, which are measuredsignals that determine the response of a semiconductor having aphotoactive layer. These measurements can be used to determine theextinction coefficient, absorbance, and absorptivity of the sample. FIG.19B shows the calculated absorptivity spectrum, a(E), using the relation

$\begin{matrix}{{a(E)} = {1 - \frac{T(E)}{1 - {R(E)}}}} & (1)\end{matrix}$

where T(E) is the transmittance and R(E) is the reflectance, all as afunction of energy E. We note that the absorptivity spectrum is often acritical parameter used in optoelectronic device modeling.

By contrast, a monochromatic light source, such as a laser that operatesin continuous wave (CW) or pulsed mode, may be used to measuresteady-state and time-resolved photoluminescence as well as thethickness of samples. FIG. 20A shows an example data set of aphotoluminescence spectrum collected using one configuration of the toolwith a CW laser light source for photoexcitation and a linearcharge-coupled device (CCD) with a diffraction grating as a detectionsystem. FIG. 20B shows a time-resolved photoluminescence decay traceusing a pulsed diode laser as an excitation source and an avalanchephotodiode (APD) paired with a time-correlated single photon counter asthe detection system.

It is significant to note that the two data sets in FIGS. 19A-20B aretypically collected on separate instruments. However, in accordance withthe concepts, techniques, and systems described herein, these data setsmay be collected using a single probe head to which multipleillumination optical assemblies (e.g. providing a broadband light sourceand a CW laser light source) and multiple collection optical assemblies(e.g. collecting spectrally dependent data and photon counts) aresimultaneously coupled. If these optical assemblies share a focal point,then these data may be further spatially and/or temporally correlated toa high precision, unlike prior art systems. Thus, the probe headincludes means for concurrently making measurements of a semiconductorusing one or more broadband light sources and one or more monochromaticlight sources (e.g. a laser light source).

In addition to the single data sets that can all be measured with thisone tool, multiple data sets can be collected simultaneously orsequentially to obtain inputs into theoretical device models. Forexample, semiconductor recombination rate constants such as k₁, k₂^(ext), and k₃ which correspond to non-radiative, first-order (i.e.Shockley-Read-Hall) effects; the external radiative, second order (i.e.bimolecular) effects; and non-radiative, third-order (i.e. Auger)effects can be measured with intensity-dependent, time-resolved PL orquantum efficiency measurements (shown in FIGS. 21A and 21Brespectively). These values, along with the absorptivity spectrum andthe film thickness, can be used as inputs into a detailed balance devicemodel.

In FIG. 22 is shown a flowchart of a method of determining physicalparameters of a semiconductor sample according to an embodiment. Themethod begins with accepting the sample into a measurement device, suchas the device shown in FIGS. 2A-3B above. In particular the sample maybe placed onto a sample bed.

The method continues with concurrently exposing the semiconductor sampleto a plurality of light sources. The light sources may be,illustratively, broadband or monochromatic light sources as describedabove in connection with FIG. 19A-20B, and exposure may be performedusing optics and optical assemblies as described in any of the aboveembodiments.

The method proceeds with concurrently detecting light from the pluralityof sources. Detecting may be performed using optical assemblies anddetectors as described in any of the above embodiments.

Finally, the method concludes with determining a range of physicalparameters of the semiconductor sample. This latter determining processmay be accomplished using hardware, or a combination of hardware orsoftware, that is integral with or coupled to the measurement device,using data analysis techniques known in the art that are applied to thedetected light.

As described above in connection with FIG. 17 , the semiconductor samplemay comprise a plurality of partially completed semiconductors. Inparticular, the partially completed material or device may be a solarcell, a light-emitting diode, an integrated circuit, a photodetector, ora laser, among others that are known to persons having ordinary skill inthe art. Thus, the method may include accepting a plurality of partiallycompleted semiconductors, and determining the range of physicalparameters for each such partially completed semiconductor.

Various embodiments of the concepts, systems, devices, structures andtechniques sought to be protected are described herein with reference tothe related drawings. Alternative embodiments can be devised withoutdeparting from the scope of the concepts, systems, devices, structuresand techniques described herein. It is noted that various connectionsand positional relationships (e.g., over, below, adjacent, etc.) are setforth between elements in the following description and in the drawings.These connections and/or positional relationships, unless specifiedotherwise, can be direct or indirect, and the described concepts,systems, devices, structures and techniques are not intended to belimiting in this respect. Accordingly, a coupling of entities can referto either a direct or an indirect coupling, and a positionalrelationship between entities can be a direct or indirect positionalrelationship.

As an example of an indirect positional relationship, references in thepresent description to forming layer “A” over layer “B” includesituations in which one or more intermediate layers (e.g., layer “C”) isbetween layer “A” and layer “B” as long as the relevant characteristicsand functionalities of layer “A” and layer “B” are not substantiallychanged by the intermediate layer(s).The following definitions andabbreviations are to be used for the interpretation of the claims andthe specification. As used herein, the terms “comprises,” “comprising,“includes,” “including,” “has,” “having,” “contains” or “containing,” orany other variation thereof, are intended to cover a non-exclusiveinclusion. For example, a composition, a mixture, process, method,article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but can include otherelements not expressly listed or inherent to such composition, mixture,process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance, or illustration. Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “one or more”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection”.

References in the specification to “one embodiment, “an embodiment,” “anexample embodiment,” etc., indicate that the embodiment described caninclude a particular feature, structure, or characteristic, but everyembodiment can include the particular feature, structure, orcharacteristic. Moreover, such phrases are not necessarily referring tothe same embodiment. Further, when a particular feature, structure, orcharacteristic is described in connection with an embodiment, it issubmitted that it is within the knowledge of one skilled in the art toaffect such feature, structure, or characteristic in connection withother embodiments whether or not explicitly described.

For purposes of the description herein, terms such as “upper,” “lower,”“right,” “left,” “vertical,” “horizontal, “top,” “bottom,” (to name buta few examples) and derivatives thereof shall relate to the describedstructures and methods, as oriented in the drawing figures. The terms“overlying,” “atop,” “on top, “positioned on” or “positioned atop” meanthat a first element, such as a first structure, is present on a secondelement, such as a second structure, where intervening elements such asan interface structure can be present between the first element and thesecond element. The term “direct contact” means that a first element,such as a first structure, and a second element, such as a secondstructure, are connected without any intermediary elements. Such termsare sometimes referred to as directional or positional terms.

Use of ordinal terms such as “first,” “second,” “third,” etc., in theclaims to modify a claim element does not by itself connote anypriority, precedence, or order of one claim element over another or thetemporal order in which acts of a method are performed, but are usedmerely as labels to distinguish one claim element having a certain namefrom another element having a same name (but for use of the ordinalterm) to distinguish the claim elements.

The terms “approximately” and “about” may be used to mean within ±20% ofa target value in some embodiments, within ±10% of a target value insome embodiments, within ±5% of a target value in some embodiments, andyet within ±2% of a target value in some embodiments. The terms“approximately” and “about” may include the target value. The term“substantially equal” may be used to refer to values that are within±20% of one another in some embodiments, within ±10% of one another insome embodiments, within ±5% of one another in some embodiments, and yetwithin ±2% of one another in some embodiments.

The term “substantially” may be used to refer to values that are within±20% of a comparative measure in some embodiments, within ±10% in someembodiments, within ±5% in some embodiments, and yet within ±2% in someembodiments. For example, a first direction that is “substantially”perpendicular to a second direction may refer to a first direction thatis within ±20% of making a 90° angle with the second direction in someembodiments, within ±10% of making a 90° angle with the second directionin some embodiments, within ±5% of making a 90° angle with the seconddirection in some embodiments, and yet within ±2% of making a 90° anglewith the second direction in some embodiments.

It is to be understood that the disclosed subject matter is not limitedin its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The disclosed subject matter is capable ofother embodiments and of being practiced and carried out in variousways.

Also, it is to be understood that the phraseology and terminologyemployed herein are for the purpose of description and should not beregarded as limiting. As such, those skilled in the art will appreciatethat the conception, upon which this disclosure is based, may readily beutilized as a basis for the designing of other structures, methods, andsystems for carrying out the several purposes of the disclosed subjectmatter. Therefore, the claims should be regarded as including suchequivalent constructions insofar as they do not depart from the spiritand scope of the disclosed subject matter.

Although the disclosed subject matter has been described and illustratedin the foregoing exemplary embodiments, it is understood that thepresent disclosure has been made only by way of example, and thatnumerous changes in the details of implementation of the disclosedsubject matter may be made without departing from the spirit and scopeof the disclosed subject matter.

1. A device for optically measuring properties of a semiconductorsample, the device comprising: a probe head configured to accept aplurality of optical assemblies; one or more optical assemblies, eachcomprising a light source, coupled to the probe head and configured todirect light toward the semiconductor sample; and one or more opticalassemblies, each comprising a detector, coupled to the probe head andconfigured to detect light from the one or more light sources.
 2. Thedevice of claim 1 further comprising a sample bed for concurrentlyaccepting multiple samples.
 3. The device of claim 1 wherein the opticalassemblies comprise a broadband optical light source and optics fordetecting a response of a semiconductor.
 4. The device of claim 3wherein the optics for detecting a response of a semiconductor comprisesoptics for detecting a response of a semiconductor having a photoactivelayer.
 5. The device of claim 1 wherein the optical assemblies comprisea broadband light source and a detector configured to detect signalsfrom the broadband light source.
 6. The device of claim 1 wherein theoptical assemblies comprise a monochromatic light source and a detectorconfigured to detect signals from the monochromatic light source.
 7. Thedevice of claim 1 wherein the optical assemblies comprise a plurality oflight sources and a detector that is configured to detect signals frommultiple ones of the plurality of light sources.
 8. The device of claim1 wherein a number of light sources coupled to the probe head equals anumber of detectors coupled to the probe head.
 9. The device of claim 8wherein each detector is configured to detect light from a correspondingone of the light sources.
 10. A probe head comprising means forconcurrently making measurements of a semiconductor using one or morebroadband light sources and one or more monochromatic light sources. 11.The probe head of claim 10 wherein at least one of the one or moremonochromatic light sources is a laser light source.
 12. A measurementsystem comprising an interchangeable optical probe head configured toaccept multiple sources and multiple detectors thereby allowing forconcurrent measurements and imaging on multiple samples.
 13. The deviceof claim 12 further comprising a processor configured to perform datamanagement and/or a data analysis methodology applicable to anyoptically active material.
 14. A method of determining physicalparameters of a semiconductor sample, the method comprising: (a)accepting the semiconductor sample; (b) concurrently exposing thesemiconductor sample to a plurality of light sources; (c) concurrentlydetecting light from the plurality of light sources; and (d) determininga range of physical parameters of the semiconductor sample.
 15. Themethod of claim 14 wherein: accepting the semiconductor sample comprisesaccepting a plurality of partially completed semiconductors; anddetermining a range of physical parameters of the semiconductor samplecomprises determining the range of physical parameters of the pluralityof partially completed semiconductors.